V4L/DVB (8357): gspca: Perfect exposure for sn9c10x, sensor ov6650.

Signed-off-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/gspca/sonixb.c

@@ -121,8 +121,8 @@ static struct ctrl sd_ctrls[] = {
 			.id = V4L2_CID_EXPOSURE,
 			.type = V4L2_CTRL_TYPE_INTEGER,
 			.name = "Exposure",
-#define EXPOSURE_DEF 0
-#define EXPOSURE_KNEE 176 /* 10 fps */
+#define EXPOSURE_DEF  16 /*  32 ms / 30 fps */
+#define EXPOSURE_KNEE 50 /* 100 ms / 10 fps */
 			.minimum = 0,
 			.maximum = 255,
 			.step = 1,
@@ -611,8 +611,6 @@ static void setgain(struct gspca_dev *gspca_dev)
 static void setexposure(struct gspca_dev *gspca_dev)
 {
 	struct sd *sd = (struct sd *) gspca_dev;
-	/* translate 0 - 255 to a number of fps in a 30 - 1 scale */
-	int fps = 30 - sd->exposure * 29 / 255;
 
 	switch (sd->sensor) {
 	case SENSOR_TAS5110: {
@@ -621,19 +619,53 @@ static void setexposure(struct gspca_dev *gspca_dev)
 		/* register 19's high nibble contains the sn9c10x clock divider
 		   The high nibble configures the no fps according to the
 		   formula: 60 / high_nibble. With a maximum of 30 fps */
-		reg = 60 / fps;
-		if (reg > 15)
+		reg = 120 * sd->exposure / 1000;
+		if (reg < 2)
+			reg = 2;
+		else if (reg > 15)
 			reg = 15;
 		reg = (reg << 4) | 0x0b;
 		reg_w(gspca_dev, 0x19, &reg, 1);
 		break;
 	    }
 	case SENSOR_OV6650: {
-		__u8 i2c[] = {0xa0, 0x60, 0x11, 0xc0, 0x00, 0x00, 0x00, 0x10};
-		i2c[3] = 30 / fps - 1;
-		if (i2c[3] > 15)
-			i2c[3] = 15;
-		i2c[3] |= 0xc0;
+		/* The ov6650 has 2 registers which both influence exposure,
+		   first there is register 11, whose low nibble sets the no fps
+		   according to: fps = 30 / (low_nibble + 1)
+
+		   The fps configures the maximum exposure setting, but it is
+		   possible to use less exposure then what the fps maximum
+		   allows by setting register 10. register 10 configures the
+		   actual exposure as quotient of the full exposure, with 0
+		   being no exposure at all (not very usefull) and reg10_max
+		   being max exposure possible at that framerate.
+
+		   The code maps our 0 - 510 ms exposure ctrl to these 2
+		   registers, trying to keep fps as high as possible.
+		*/
+		__u8 i2c[] = {0xb0, 0x60, 0x10, 0x00, 0xc0, 0x00, 0x00, 0x10};
+		int reg10, reg11;
+		/* No clear idea why, but setting reg10 above this value
+		   results in no change */
+		const int reg10_max = 0x4d;
+
+		reg11 = (60 * sd->exposure + 999) / 1000;
+		if (reg11 < 1)
+			reg11 = 1;
+		else if (reg11 > 16)
+			reg11 = 16;
+
+		/* frame exposure time in ms = 1000 * reg11 / 30    ->
+		reg10 = sd->exposure * 2 * reg10_max / (1000 * reg11 / 30) */
+		reg10 = (sd->exposure * 60 * reg10_max) / (1000 * reg11);
+		if (reg10 < 1) /* 0 is a valid value, but is very _black_ */
+			reg10 = 1;
+		else if (reg10 > reg10_max)
+			reg10 = reg10_max;
+
+		/* Write reg 10 and reg11 low nibble */
+		i2c[3] = reg10;
+		i2c[4] |= reg11 - 1;
 		if (i2c_w(gspca_dev, i2c) < 0)
 			PDEBUG(D_ERR, "i2c error exposure");
 		break;